Summary

Intra-articular anterior cruciate ligament (ACL) cysts are rare, the pathogenesis remains unknown, with trauma often implicated.
Often asymptomatic, incidental MRI findings, 11% produce symptoms such as pain, locking or instability. Treatment of intra-articular
ganglia differs from the traditional ‘bash it with a bible’ mantra for ganglia elsewhere with surgical debridement generally
indicated for symptomatic cases. This case report describes a 43-year-old male car mechanic who presented with a symptomatic
ACL cyst diagnosed on MRI. While waiting for surgery the patient fell up his stairs at home, causing forced hyperflexion of
his knee. After an initial sharp pain, within 24 h the patient experienced complete resolution of symptoms. Postfall MRI showed
no evidence of the initial lesion, leading to our conclusion that for this patient, a fall up the stairs was the equivalent
of ‘bashing it with a bible’ for an ACL ganglion cyst of the knee.